Ink jet printers are a well-known and widely used form of printed media production. Ink is fed to an array of digitally controlled nozzles on a printhead. As the print head passes over the media, ink is ejected from the array of nozzles to produce an image on the media.
Printer performance depends on factors such as operating cost, print quality, operating speed and ease of use. The mass, frequency and velocity of individual ink drops ejected from the nozzles will affect these performance parameters.
Recently, the array of nozzles has been formed using micro-electromechanical systems (MEMS) technology, which have mechanical structures with sub-micron thicknesses. This allows the production of printheads that can rapidly eject ink droplets sized in the picolitre (×10−12 litre) range.
While the microscopic structures of these printheads can provide high speeds and good print quality at relatively low costs, their size makes the nozzles extremely fragile and vulnerable to damage from the slightest contact with fingers, dust or the media substrate. This can make the printheads impractical for many applications where a certain level of robustness is necessary. Furthermore, a damaged nozzle may fail to eject the ink being fed to it. As ink builds up and beads on the exterior of the nozzle, the ejection of ink from surrounding nozzle may be affected and/or the damaged nozzle will simply leak ink onto the printed substrate. Both situations are detrimental to print quality.
To address this, an apertured guard may be fitted over the nozzles to shield them against damaging contact. Ink ejected from the nozzles passes through the apertures on to the paper or other substrate to be printed. However, to effectively protect the nozzles, the apertures need to be as small as possible to maximize the restriction against the ingress of foreign matter while still allowing the passage of the ink droplets. Preferably, each nozzle would eject ink through its own individual aperture in the guard. However, given the microscopic scale of MEMS devices, slight misalignments between the guard and the nozzles will obstruct the path of the ink droplets. Providing alignment formations on the silicon wafer substrate for engaging complementary formations on the guard can align the nozzles and respective apertures to within 0.1 μm. However, while attaching the guard to the substrate, movement of the complementary formations into engagement with the alignment formations can damage the delicate nozzle structures.